<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../vue.js" type="text/javascript"></script>
    <style>
        .active{
            color: red;
        }
    </style>
</head>
<body>
    <div id="app">
        <h2 class="active line">{{message}}</h2>
        <h2 :class="[active, line]">{{message}}</h2> 
        <h2 :class="getClasses()">{{message}}</h2>
    </div>
    <script>
        var app = new Vue({
            el: "#app",
            data: {
                message: "message",
                active: "active",
                line: "line"
            },
            methods: {
                getClasses:function(){
                    return [this.active, this.line]
                }
            }
        })
    </script>
</body>
</html>